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Orientational order of Langmuir–Blodgett films as determined by fluorescence anisotropy (1989)

LeGrange, Jane D. ; Riegler, Hans E. ; Zurawsky, Walter P. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 90 (1989), S. 3838-3842

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The orientational order parameters 〈P2〉 and 〈P4〉, of cadmium stearate Langmuir–Blodgett multilayers have been calculated from steady state fluorescence anisotropy experiments. It has been shown that it is valid to model the polarization components using the assumptions that the fluorescent probes are axially symmetric, the film is azimuthally symmetric within the plane, and that the rotational motion is slow enough to be neglected. Although the data do not preclude a dependence of anisotropy on thickness, within the sample-to-sample variations, there is no significant effect of thickness on orientational order. The order parameters for newly deposited films are 〈P2〉=0.33 and 〈P4〉=0.02. The orientational order decreases in the first 600 h after deposition, and then remains stable for at least several months.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.455789

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Impedance spectroscopy of reactive polymers. 3. Correlations between dielectric, spectroscopic, and rheological properties during cure of a trifunctional epoxy resin (1996)

Mijović, Jovan ; Andjelic, Sas̆a ; Fitz, Benjamin ; [et al.]

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 379-388

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ISSN: 0887-6266

Keywords: impedance spectroscopy ; reactive polymers ; rheological properties ; trifunctional epoxy resin ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: An investigation was carried out of correlations between dielectric, vibrational spectroscopic, and rheological properties during cure of a thermoset formulation composed of trifunctional epoxy resin and tetrafunctional amine. Experimental techniques utilized include impedance spectroscopy, near-infrared spectroscopy, steady shear, and dynamic mechanical measurements. Reaction kinetics obtained from dielectric and spectroscopic results were in excellent agreement. Gelation and vitrification times determined by dielectric and rheological measurements were also found to agree very well, despite the empirical nature of such correlations. A characteristic pattern in plots of imaginary impedance as a function of reaction time was reported for the first time in the open literature, and it was suggested that it could be used to identify gelation and vitrification during the network formation. A realization of the full potential of dielectric impedance spectroscopy in monitoring the progress of chemophysical changes in reactive polymers, however, hinges upon a development of fundamental scientific correlations between dielectric and chemorheological phenomena during cure.

Additional Material: 9 Ill.